1. Field of the Invention
The present invention relates to the manufacture of molded glass articles such as bottles, and the like and more particularity to the use of blow molding gases cooled in a heat-exchanger by a cryogenic fluid which is thus vaporized and recovered to be used in another step of the manufacture of said molded glass articles.
2. Prior Art :
In the manufacture of molded glass articles, such as bottles and the like, a bath of molten glass is typically made in a melting furnace using generally but not necessarily air fuel burners or in some instances, oxygen enriched air burners, or oxy-fuel burners to maintain the glass in a molten state. Said molten glass is refined in a refining station and then conveyed in at least one forehearth connected to a forming machine in which hollow glass articles are formed and blown. Then the articles are transferred on conveyor belts to a lehr. After annealing, said articles are packed in a packaging station. In some instances, said articles are filled with liquid, inerted and sealed prior to their transfer to the packinging station.
In the forming station, it is conventional to use a cooling medium to cool the blank molds in which a parison of glass is formed and the finishing molds in which it is expanded to the desired final shape. Such a cooling medium is usually compressed air at a temperature of ambient air or higher. This compressed air is injected inside the freshly molded articles to blow them and hasten their solidification. The hollow articles are removed as quickly as possible from their molds and then placed on a conveyor belt to be flame-polished, if necessary.
A process of this type is disclosed in U.S. Pat. No. 3,233,416, Rainwater et al. The air is carried through a vortex tube and thus cooled, said air being used as blowing air and for cooling air that is supplied to a jacket surrounding the mold cavity.
However, this system has several drawbacks : Air is first dryed, then compressed and then cooled in a heat exchanger and then conducted through a pipe in the vortex tube, said tube separating the supplied air into hot and cold fractions, the hot fraction being recycled through a second heat exchanger which is connected to an air storage tank. The cold fraction injected through a pipe is used firstly to blow (and cool) the parison against the wall of the mold cavity, said fraction being discharged at a temperature of about 20.degree. F. and secondly, after escaping from the mold cavity, to cool the said pipe or at least insulate it, while said air is still at a substantially lower temperature than atmospheric temperature.
It is clear, from this brief description, that this system is complicated, whith a least two heat exchangers and a vortex device in the pipe between the source of compressed air and the mold cavity and has also a poor output, namely because an important part of the compressed air is heated in said vortex device.
More recently, it has been proposed in U.S. Pat. No. 4,553,999 to use cold cryogen vapors or a mixture with air to blow the cool hollow glass articles to hasten their solidification. However, the use of a continuous injection of cold cryogen vapors generates ice crystals which rapidly block up the injection pipe through which the vapors are blown.